There is not a terse or laconic answer to this question.
Having said that, this is as concise an answer I would propound, 'LCHF'
Eat as few carbs as you can and enjoy butter, cheese, double cream, steak, chicken, salmon, tuna...
There are so many great sites to learn about what you can eat with impunity and those you should avoid like the plague
Forget about bread, potatoes, (chips, crisps, mash, roasted, etc,) rice, cereals, pulses, pizza, take a-ways, most ready meals, cakes biscuits. Sounds like there is nothing you CAN eat. Trust me Laconic, there is a whole new world of great, healthy, tasty, filling foods waiting for you to discover.
Read the labels on everything you buy and choose wisely what suits you.
How low is low carb? That's entirely up to you. Start off at say 100g a day and see how you go.
Beware of any diet foods and all sauces, if it is low fat the chances are it is full of sugar to make it taste nice.
Cream is better for you than milk, full fat, semi OR skimmed.
Butter is your friend.
Others here will be happy to point you in the right direction I'm sure.
Po